1. Field of the Invention
The present invention relates to the field of providing blanket gas, also referred to as shielding gas or active gas, to a welding point in an electrical welding apparatus, particularly to a method and device for controlling blanket gas (shielding gas; active gas) flow in various stages of a welding operation.
2. Description of the Related Art
For electrical welding operations where the welding point is to be provided with a blanket of inert blanket gas, it is common to provide the blanket gas from a centralized blanket gas supply installation, or from a gas cylinder located in the vicinity of the welding machine unit of the welding apparatus. The blanket gas provided by the supply installation or the gas cylinder typically is provided with a gas pressure that exceeds the pressure at which the blanket gas can be controlled by the blanket gas control means of the welding apparatus. In order to reduce the pressure to level at which the gas conveniently can be delivered to the welding apparatus, and be controlled by a control valve in the welding apparatus switching on and off the flow of blanket gas, a pressure reduction device is inserted in the blanket gas supply line in a location proximal to the gas cylinder or the gas supply installation. Thus, a section of the gas supply line, in which the gas is provided at a lower gas pressure than in the gas supply installation or gas cylinder, exists between the pressure reduction device and the welding machine itself. Typically, this “low pressure” section of the supply line is of a considerable length, in order to allow practical use of the welding machine unit, which often is required to be easily relocatable in order to reach differently located areas at which the welding work is to be performed. Further details with regard to the aspects of the low pressure supply line and the control of blanket gas supply for an electrical welding apparatus is provided in the present applicant Norwegian patent application no. 20021557, and corresponding applications claiming priority from the aforementioned application.
For the welding process requiring an appropriate supply of blanket gas to maintain a consistent quality of the welding work there is performed, the correct supply of blanket gas is dependent on number of different factors. One of these is the electrical current of the welding art established between the welding electrode and the electrically conductive object being welded, while another important factor is the design of the electrical welding machine itself, particularly with regard to how the supply of the blanket gas is controlled with respect to the actual welding operations being performed. The latter is also important with regard to the economy of operating an electrical welding apparatus, as the consumption of blanket gas for welding operations is an important factor in the overall economy of an operator of a facility that provides welding services based on electrical art welding, for whom it will be important to control the consumption of blanket gas in order to minimize the consumption of possibly expensive blanket gas, while still meeting the requirements to the quality of the weld produced during the welding operation.
The flow of blanket gas to the weld spot typically is controlled by actuating a blanket gas valve in the welding machine from a control signal that controls the application of a voltage to the welding electrode or the motor of the feed arrangement to feed a continuous electrode in case of a MIG welding apparatus, or a signal that is related to any of the aforementioned. Upon the actuation of the blanket gas valve in the welding apparatus, which opens for gas flow to the welding spot by way of a gas supply line in a flexible hose for supply of both gas and electrical power to the welding area, the blanket gas flows at a rate set by a flow control device that typically is arranged in conjunction with the pressure control device mentioned above. With the flow control system disclosed by Norwegian patent application no. 20021557, the flow of blanket gas is dynamically controlled as a function of the feed rate of the continuously fed welding electrode wire, the feed rate preferably being indicated by a voltage applied to an electrical motor of the feeding arrangement to control the feed rate, or as a function of a welding current setting made by an operator or by a system operating the welding machine. By the device and method of Norwegian patent application no. 20021557, the supply of blanket gas to where the welding work is being done may be optimized with regard to the supply of welding gas as the actual welding work proceeds.
A shortcoming in the arrangements and methods for supply of blanket gas for electrical welding in an electrical welding machine remains, as such prior art arrangements and methods are not concerned with the effects of the blanket gas supply rate prior to or at the time when heat is being generated in the initial face of a particular welding operation.